Study On Control Strategy For Micro-grids’Interconnection During Network Restoration

Due to its strong capability of autonomy and self-healing, micro-grid is an effective solution for integration of distributed generation. It can operate steadily at the island mode for a long time and switch between island mode and gird-connected mode smoothly. Under situations of massive faults in distributed network, micro-grid is able to maintain continuous power supplies for loads within its scope. This advantage can be increasingly magnified as the number of micro-grid grows. Under emergencies, independent micro-grids can further enlarge the power supply region through interconnecting with each other, which provides a new insight for achieving self-healing from LV to MV in distribution network. In addition, interconnection will improve the operation quality and then the power quality of user side compared to independent micro-grid. This thesis focuses on the control strategy for micro-grids’ interconnection, tries to combine interconnection technology with self-healing issue in distribution network and proposes a new solution for networks’self-healing based on it. This thesis can be organized as follows:First, the fundamentals of multi-microgrids’interconnection are analyzed. A multi-layer control structure for distributed network is presented and then two controllable micro-sources in micro-grid, storage devices and diesel generators are studied. Detailed models are built for each micro-sources and control schemes for both are analyzed in depth. Second, the criterions for stable interconnection between micro-grids are studied. A criterion considering low-frequency risk and a criterion considering both power fall of distributed generation and adapting range of storage are presented respectively. Since there are two stages of operation, at the transition and after the transition, control schemes for interconnecting micro-grids at the transition stage and control schemes for interconnection micro-grids based on automatic generation control are presented respectively as well. At last, the application process of interconnection technology in network’s self-healing is demonstrated. The feasibility of the aforementioned opinions is verified through simulation analysis.